The advent of digital circuits has caused great progress to be made in measurement and control equipment in the last few years. Such digital circuits require an increased number of more accurate and versatile sensors for physical quantities of all types. The development of digital systems coincides with the introduction of optical fibers and the optoelectronic transmitting and receiving elements associated therewith. The advantages of such systems are well known: They include a wide bandwidth, electrical isolation, relative insensitivity to electric noise, the ability to withstand extreme temperature changes and explosive or corrosive environments, low weight and small space requirements.
If a conventional electronic sensor is used, a transducer must be supplied which changes the electrical output signal of the sensor into an optical signal. The optical signal is then transmitted through the fiber to an indicator or to the control unit. It must then be converted back to an electronic signal. Thus there must be at least two transducing stages. To eliminate this need and to improve the accuracy, linearity and stability of measurement, it is desirable to have sensors which immediately translate the quantity to be measured into a suitable light signal.